A numerical investigation of hydraulic fracturing on coal seam permeability based on PFC-COMSOL coupling method

Abstract

Hydraulic fracturing and permeability enhancement are effective methods to improve low-permeability coal seams. However, few studies focused on methods to increase permeability, and there are no suitable prediction methods for engineering applications. In this work, PFC2D software was used to simulate coal seam hydraulic fracturing. The results were used in a coupled mathematical model of the interaction between coal seam deformation and gas flow. The results show that the displacement and velocity of particles increase in the direction of minimum principal stress, and the cracks propagate in the direction of maximum principal stress. The gas pressure drop rate and permeability increase rate of the fracture model are higher than that of the non-fracture model. Both parameters decrease rapidly with an increase in the drainage time and approach 0. The longer the hydraulic fracturing time, the more complex the fracture network is, and the faster the gas pressure drops. However, the impact of fracturing on the gas drainage effect declines over time. As the fracturing time increases, the difference between the horizontal and vertical permeability increases. However, this difference decreases as the gas drainage time increases. The higher the initial void pressure, the faster the gas pressure drops, and the greater the permeability increase is. However, the influence of the initial void pressure on the permeability declines over time. The research results provide guidance for predicting the anti-reflection effect of hydraulic fracturing in underground coal mines.

A comprehensive review of numerical simulation methods for hydraulic fracturing

“…This software can be coupled with particle flow code to study the hydraulic fracturing mechanism and the flowing ability of the coal reservoirs. 134 Jafari et al 135 combined the thermo-mechanical, hydrological, and heat transfer concepts for the numerical simulations. This comprehensive model allows for studying fluid flow within porous media by considering mechanical deformation, fluid movement in porous materials, and heat transfer phenomena.…”

“…used COMSOL multiphysics to study the influence of coal bed methane permeability, initial gas pressure, and fracture length on methane production from a fractured well. This software can be coupled with particle flow code to study the hydraulic fracturing mechanism and the flowing ability of the coal reservoirs 134 . Jafari et al 135 .…”

Mechanism and Model Analysis of Ultralow-Temperature Fluid Fracturing in Low-Permeability Reservoir: Insights from Liquid Nitrogen Fracturing

“…The factors affecting the low-temperature fluid fracturing effect on coal are complex and diverse and are generally divided into external factors (temperature difference, fracturing times, time) [46][47][48][49][50][51] and the internal factors of the coal itself (coal rank, water content, pore structure, mechanical properties of the coal body itself, etc.) [52,53].…”

Analytical Damage Model for Predicting Coal Failure Stresses by Utilizing Acoustic Emission

“…In recent years, hydraulic flushing and water injection have been widely used to alleviate coal and gas outbursts, reduce coal dust, and prevent coal seams from spontaneous combustion [6][7][8][9][10][11]. Coal seams undergo significant changes due to hydraulic measures, resulting in significant changes in their mechanical characteristics and geophysical properties as a result [12][13][14][15]. In the application of geotechnical engineering, water relates to geological disasters, since it affects the mechanical characteristics of coal [16,17].…”